Potash, Pee and Comfrey

I like her writing, she knows how to connect the big issues with the food we actually eat, and hopefully enjoy.

I’ve spent a lot of time thinking about where to obtain the macro nutrients N (nitrogen), P (phosphorus) and K (potassium or potash) for The Oak Tree Low Carbon Farm. I’m “growing without the use of artificial pesticides or fertilizers” (I don’t pay the relevant certifying bodies, so I can’t use the “O” word). so buying chemical fertilizers is out. They are bad for the biodiversity of the soil and bad for plants anyway, so it isn’t a big dilemma for me.

But the question remains – I am exporting veg from the site, so where do I get N, P and K from to grow the next round of veg? And when I start exporting fruit and eggs from the site? What about the pigeons that get shot and eaten.

It is great to see that Rose Prince highlighted the human waste recycling question. This was the solution used in traditional Chinese agriculture, as described in the classic tome Farmers of Forty Centuries, and no doubt in countless other systems of agriculture, including the traditional back garden privy here in the UK. A neighbour at The Oak Tree recalls digging the night soil into the animal manure heap as a boy, leaving a marker to indicate where so the next lad with that particular responsibility could choose a different spot.

But back to The Oak Tree. The question of recycling human waste isn’t one I can tackle wholesale on my own. It wouldn’t be a great marketing move to request that customers drop off their night soil when they buy their veg 🙂 Now (and don’t be shocked, please, it is quite hygienic) I do pee into a glorified bucket on the farm and then use it on the comfrey bed. I use hand sanitiser and clean everything scrupulously from time to time.

Comfrey is deep rooted and needs a great deal of potassium, and pee provides it. I don’t eat my comfrey, but I will use it as a mulch around plants, but only with a very long delay between applying pee and harvesting the leaves. And even then I won’t let the leaves touch anything I am planning to harvest, they will be spread around the plants, on the ground.

But this is just me, unless kind visitors are willing to donate some potash (and some have been 🙂 According to Iain Tolhurst, co-author of Growing Green, a book I refer to a lot for The Oak Tree, much of the potassium needed for veg is simply locked up in soils with any clay content, and these can be released from the top and sub soil with microbial activity. I was astonished to read this, but Tolhurst Organics market garden is living proof that it can work. So for the moment, I am trying these techniques and I’ll keep testing the soil…